1. Field of the Invention
The invention in general relates to temperature sensors, and particularly to apparatus which includes an elongated sensor for placement against a device to be monitored, the apparatus being capable of determining an abnormal hot spot at any point along the elongated sensor.
2. Description of the Prior Art
In the field of diagnostics, various sensors are generally provided to monitor different predetermined parameters of an operating on-line system. A common measurement for a typical system may include one or more temperature readings which are monitored to see that they do not exceed predetermined values, dependent upon the operating system.
A typical temperature sensor may include a small thermistor or thermocouple which provides an electrical output signal proportional to the measured temperature. Some systems, however, preclude the use of such sensors in view of the extremely hostile electrical environment to which they are subjected. By way of example, modern electric generators such as those driven by steam turbines have the capacity to carry several thousand amperes of current in their stator windings. In view of the extremely high and varying magnetic fields caused by this current, as well as voltages measurable in the tens of kilovolt range, temperature sensors having long electrical output leads cannot be placed directly on the windings. Sensors are generally located at some distance from the windings so as to obtain a temperature reading by secondary measurements of the cooling water or cooling gas normally passed through such windings.
Under certain circumstances, due to the distant placement of the sensors and the indirect temperature measurement, a severe condition may already exist before detection is possible. Due to some abnormal operating condition, a hot spot may be generated in the winding, raising the localized temperature to an abnormal value. Although the hot spot will cause a temperature rise in the cooling medium, the rise in temperature as presently detected may vary as a function of the location of the hot spot.
The present invention obviates the indirect method of temperature sensing and will immediately give an indication of an abnormal hot spot. Further, the apparatus can be constructed and arranged to give the location of the hot spot as well as its temperature.